The fatal crash of a commercial airliner, American Eagle Flight 4184, an ATR-72 aircraft, on Oct. 31, 1994 near Roselawn, Ind. with the loss of all 68 on-board and the more recent crash on Feb. 16, 2005 of a Cessna Citation corporate jet owned by Circuit City during approach to the Pueblo, Colo. airport killing the two pilots and six other people on-board, both events attributed to aircraft icing by the National Transportation Safety Board (NTSB), emphasize the importance of knowing when ice is accreating on an aircraft. Icing in these cases caused detrimental loss of control and a dramatic increase in aircraft stall speed, respectively, which in turn went unrecognized leading to the fatalities. Besides these two examples for manned aircraft, there have been additional crashes of unmanned aircraft due to icing, for example, while being used by various nations in the Kosovo conflict. It is also important to know what type of ice is accreating on an aircraft or unmanned vehicle and at what rate for the added weight of accumulated ice may effect aircraft performance and its presence may also significantly interfere with the generation of lift by altering the airfoil shape or causing loss of control surface effectiveness.
Ice principally occurs from supercooled water droplets in the atmosphere that freeze on the aircraft at atmospheric and aircraft surface temperatures in the range from 0° C. to −25 C and at altitudes between sea level and 22,000 feet as discussed in the paper entitled “Meteorological Conditions During the Formation of Ice on Aircraft”, Samuels, T. L., NACA TN No. 439, December 1932 though on occasion ice occurs outside these ranges. Two forms of ice may be encountered: glaze or rime ice. Glaze ice is clear in appearance and weighs 0.98-0.99 g/cubic cm, while rime is white and opaque in appearance and weighs between 0.35-0.55 g/cubic cm depending on aircraft Mach number at which it was accreated. It should be noted that glaze ice will add a substantially higher weight penalty than rime ice for the same volume of accreated ice. The present invention is designed to operate over an extended temperature range from above 0 C to −40 C to encompass all probable conditions for icing.
Numerous methods and apparatus have been patented for the detection of ice on the exterior surfaces of an aircraft and for the determination of ice thickness. In the review of prior art that follows, prior art is grouped by the method used to determine ice presence and thickness. Major groupings to be considered include those that utilize acoustic/ultrasound, pneumatic, electrical, heat, light, mechanical, radiation by electrical means, time domain reflectometry or transmission line approaches. Other groupings include capacitance or impedance approaches for ice detection with a review of those two categories following the first grouping. The purpose in reviewing such a large, far ranging portion of prior art, as is done below, is to demonstrate that no patent in the prior art for ice detection provides a measurement approach that operates continuously in time to determine the type of ice being accreated, glaze or rime, or its thickness which is a claim of the present invention. The review of prior art also demonstrates that no patent in the prior art for ice detection provides an independent measurement that guarantees that the contaminant being accreated is known to be ice and only ice; another claim of the present invention.
As will be described in more detail in the following, the present invention provides a continuous means to identify the presence of ice, thickness of ice, thickness time history of ice, and type of accreated ice, glaze or rime, as well as providing means to discriminate between glaze ice, rime ice, rain water, deicing fluid, snow, or air. In addition, the present invention includes a separate test of the contaminant to reconfirm that what is initially detected to be ice is indeed ice and only ice and not something else. This is done by confirming a particular signature that ice has in complex dielectric space; a semicircular locus. Prior art is now reviewed in the sequence of groupings discussed above.
Prior art for ice detection includes acoustic/ultrasound systems of Hsu et al. in U.S. Pat. No. 5,095,754 and Vopat in U.S. Pat. No. 6,731,225. Prior art utilizing pneumatic principles is that of Catchpole in U.S. Pat. No. 3,976,270, Edgington in U.S. Pat. No. 3,996,787, U.S. Pat. No. 4,053,127 and U.S. Pat. No. 4,095,456, and Blaha in U.S. Pat. No. 5,301,905. Prior art utilizing electrical principles is that of Gerardi et al. in U.S. Pat. No. 5,206,806, by Inkpen et al. in U.S. Pat. No. 5,394,340 and U.S. Pat. No. 5,621,332, by Corbi in U.S. Pat. No. 5,621,400 and by Petrenko et al. in U.S. Pat. No. 6,653,598.
Prior art utilizing the principle of internal heat transfer is that by Sabin in U.S. Pat. No. 4,819,480, by Freeman in U.S. Pat. No. 5,140,135, by Ortolano in U.S. Pat. No. 5,521,584 and by Keyhani in U.S. Pat. No. 6,328,467. Prior art utilizing the principle of light reflection and/or obturation is that by Kapany et al. in U.S. Pat. No. 3,045,223, by Burns in U.S. Pat. No. 5,760,711 and by Anderson et al. in U.S. Pat. No. 6,425,286 and U.S. Pat. No. 6,430,996. Prior art utilizing mechanical vibration or compressive strength principles is that by Marxer et al. in U.S. Pat. No. 4,553,137, by Goldberg et al. in U.S. Pat. No. 4,745,804 and by Cronin in U.S. Pat. No. 6,320,511.
Prior art utilizing radiation by electrical means is that by Magenheim in U.S. Pat. No. 4,054,255, by Seegmiller in U.S. Pat. No. 5,523,959, by Kates et al. in U.S. Pat. No. 5,652,522, by Stolarczyk et al. in U.S. Pat. No. 5,686,841 and by Anderson et al. in U.S. Pat. No. 6,166,66. Prior art utilizing time domain reflectometry (TDR) or transmission line principles is that by Yankielun et al. in U.S. Pat. No. 6,608,489 and by Arndt et al. in U.S. Pat. No. 6,995,572.
Prior art utilizing capacitance principles is that by Weinstein in U.S. Pat. No. 4,766,369, by Gerardi et al. in U.S. Pat. No. 5,191,791, U.S. Pat. No. 5,398,547, U.S. Pat. No. 5,551,288 and U.S. Pat. No. 5,874,672 and by Baas et al. in U.S. Pat. No. 6,879,168. Prior art utilizing impedance principles is that by Klieve in U.S. Pat. No. 2,432,669, by Stolarczyk et al. in U.S. Pat. No. 5,474,261, by Rauckhorst et al. in U.S. Pat. No. 5,569,850, by Inkpen et al. in U.S. Pat. No. 5,621,332, by Codner et al. in U.S. Pat. No. 5,955,887 and by Wallace et al. in U.S. Pat. No. 6,384,611.
The ultimate ice detection system for an aircraft in flight should be able to detect the presence of ice when it first starts to accreate on the aircraft and to provide a continuous measurement of ice thickness with time after icing onset or after a deicing cycle. It should be able to discriminate between different types of contaminant that might overlay the sensor such as ice, rain water, deicing fluid, or snow so that it may be sure that it is ice and not, for example, rain water or other contaminant. It should be able to identify the type of ice that is accreating: glaze or rime. It should have integral to itself a means to absolutely confirm that it is ice that is accreating rather than just being an approach that assumes without confirmation that the contaminant is ice. Finally, if it is to be used to detect contaminant build-up on an aircraft sitting at a gate on the ground before takeoff or after deicing on the ground, it should have the ability to provide presence and thickness measurements for ice, snow and sleet should these be the contaminating agents that are being deposited. The features of prior art patents identified in the four preceding paragraphs will now be compared to the desired characteristics listed here for the ultimate ice detection method for an aircraft in flight.
Such a comparison has been made and it shows that sixteen of the forty one prior art patents only detect the presence of ice and nothing else. An additional twelve patents detect the presence of ice and provide thickness values and thickness time histories. The remaining thirteen patents detect the presence of ice, provide ice thickness and thickness history and say they are able to discriminate between types of contaminants including ice, rain water and deicing fluid. But none of the patents is found to be able to continuously identify the type of ice, glaze or rime, or provide a continuous measurement of ice thickness or that ice is accreating nor do any of the patents provide a means for an independent crosscheck that the contaminant is indeed ice. The following thirteen patents of the forty one patent set are believed to provide presence, intermittent thickness, intermittent thickness time history and discrimination between ice, rain water and deicing fluid: U.S. Pat. No. 5,095,754, U.S. Pat. No. 5,394,340, U.S. Pat. No. 5,398,547, U.S. Pat. No. 5,474,261, U.S. Pat. No. 5,551,288, U.S. Pat. No. 5,569,850, U.S. Pat. No. 5,621,332, U.S. Pat. No. 5,686,841, U.S. Pat. No. 5,760,711, U.S. Pat. No. 5,874,672, U.S. Pat. No. 6,384,611, U.S. Pat. No. 6,608,489 and U.S. Pat. No. 6,995,572. The present invention will now be described and shown to meet the requirements discussed above for the ultimate ice detection system for use in flight. The present invention provides an indication of ice onset, ice thickness, and ice thickness time history and discriminates between contaminants and type of ice, glaze or rime, as well as providing an independent crosscheck that ice is the contaminant.